The invention relates to a steam generator, particularly for a pressurized water nuclear reactor.
In the nuclear industry, steam generators are known, which are used in conjunction with pressurized water reactors and whereof one per se known type is described with reference to FIG. 1. FIG. 1 shows the enclosure 1 of the reactor containing core 2 and in which circulates, on the one hand, at 3 the rising hot water leaving the core in the direction of arrow F and, on the other hand, the descending cold water circulating between envelope 1 and the reactor basket 4.
In per se known manner, steam generator 5 has a water box 6, in which circulates the water coming from reactor 1 whilst, above said water box 6, there is a ferrule 7 traversed by secondary water entering at 8 and leaving at 9 with respect to said secondary ferrule 7. A pipe 10 connects reactor 1 to the water box 6 and has two concentric annular passages, namely a central passage 11 by which the hot water enters water box 6 and a peripheral passage 12 by which the cold water from water box 6 leaves and returns to the reactor 1 between the basket and the enclosure to be reinjected at the bottom of the core.
In known manner, water box 6 is separated from the secondary ferrule 7 by a tube plate 13, in which are vertically installed a certain number of inverted U-shaped heat exchange tubes 14 and traversed by primary fluid. The water box 6 is subdivided into two parts, namely a hot compartment 15 and a cold compartment 16. The secondary water which travels in rising manner within the secondary ferrule 7, heats and evaporates progressively whilst rising along the U-tubes 14.
In all existing steam generators of loop reactors, such as described hereinbefore, or integrated reactors of the CAP type, for which the primary vessel acts as a water box, the secondary ferrule 7 is directly welded to tube plate 13, which is jammed on to the water box 6. As a result of the large pressure difference (approximately 100 bars) to which the tube plate 13 is exposed, stresses are accumulated in the angular connecting zone of said plate 13 to secondary ferrule 7. In order not to weaken this zone, it is consequently not possible to perforate the plate too near to its junction with the secondary ferrule 7 in order to install tubes there, which increases the overall dimensions of the steam generator in the manner shown in FIG. 2, where it is possible to see that a minimum space e is necessary between the side wall of the secondary ferrule and the first tube 14 installed in the tube plate 13.
Moreover, the secondary part of such a steam generator cannot be disassembled and it is therefore very difficult to repair it or even clean it when necessary after a certain period of operation and its inspection whilst in service is a complicated, dangerous operation.